20–120 cm high; erect, cylindrical, much branched; abundant white hairs that are long and straight, but slightly downward-pointing; often a reddish purple ring or patch at the junction of a new stem developing from an older stem; upper stems terminate in racemes of yellow flowers

Leaves:

Alternate, dissected, dentate or serrate; upper leaves may clasp the stem, lower leaves have petioles and ovate, oblanceolate, or obovate in shape

Flowers:

4 Yellow petals, 6 stamens, and a single green pistil in the center

Fruits / pods:

Silique tapers into a short beak; several fine nerves running along the length of its surface, which is slightly pubescent or hairless; seedpods, erect or spread outward, but they do not droop downward; tiny dark brown or black spherical seeds

The standard author abbreviation Besser is used to indicate Wilibald Swibert Joseph Gottlieb von Besser (1784 – 1842), an Austrian-born botanist who worked most of his life within the territory of Western Ukraine.

In Israel there are many species belonging to the family of Cruciferae which have yellow flowers and seeds with a pungent flavor. Among these the species Sinapis arvensis is very widespread. This is called in the Mishnah lafsan ("charlock") and it was laid down that "mustard and charlock, although resembling one another, do constitute kilayim" (Kil. 1:5), Kil'ayim כלאים, the fourth tractate of Seder Zeraim ("Order of Seeds") of the Mishnah and of the Talmud (Kil'ayim deals chiefly with rules regarding forbidden mixtures in agriculture, clothing and breeding (Leviticus 19:19; Deuteronomy 22:9–11)).
Many have supposed that the charul (Greek, φρύγανα άγρία, similar to a term meaning "a rough dry stick") may probably be the Sinapis arvensis, which is a pernicious weed abounding in corn-fields.
The word خردل khardul is applied in all old Arabic works, to species of mustard and it is not unlike the kharul or charul, of the Bible.

Bible Resources:

Job 30:7
They brayed among the bushes and huddled in the undergrowth ) Charul, חרול).

Proverbs 24:31
thorns had come up everywhere, the ground was covered with weeds, and the stone wall was in ruins.

Zephaniah 2:9
Therefore as I live," saith the LORD of hosts, the God of Israel, "surely Moab shall be as Sodom, and the children of Ammon as Gomorrah" even the breeding of nettles and salt pits, and a perpetual desolation. The residue of My people shall despoil them, and the remnant of My people shall possess them."